This invention relates to an air buffer type apparatus for key durability testing and more particularly to a testing apparatus that can effectively simulate a real key stroke operation.
Key durability testing is one of important quality control items for keyboards used in computers, notebook computers and the like. The main purpose of such testing is to check the durability of the spring or the loading rubber installed below the key. Conventionally, testing apparatus in the art can be generally classified into a cam type and a pneumatic type.
FIG. 1 shows the structure of a conventional cam type key durability testing apparatus. It includes a cam 10, a linkage bar 11 and a movable rack 13 for generating vertical up and down displacements. As shown, a plurality of depression bars 131 are provided below the movable rack 13 and above the testing keys 200. When the cam 10 is activated to rotate, the depression bars 131 will be moved downward to further depress the key top 100 and the loading rubber 101 of the key 200. Hence, by means of the reciprocal motion of the depression bars 131 driven by the cam 10, key durability test may thus be preformed. However, the displacement of the depression bars 131 in the above structure is fixed. To get a best test result, the lowest position of the depression bars 131 should match the ideal lowest position of the key 200. However, in an actual testing, the preferred situation would seldom be achieved. For instance, it could happen that, at the moment of the key 200 reaching the lowest position, the depression bar 131 does not stop but keeps moving downward to produce a maximum test pressure greater than a preset value. Such a situation would render a lower durability result than it should be. In another example, the depression bar 131 might reach its lowest position before the key 200 can mimic a real lowest depression position, so that a fake higher durability result may be obtained.
Moreover, the fixed displacement operation may result in a state shift of the apparatus after each operation. Therefore, it can be foreseen that a tedious and time-consuming machine adjustment is required before each test operation. Furthermore, the operation obeying fixed displacement guideline does not accurately simulate human typing operation by fingers. A normal finger action might be better mimicked by a maximum resistant force mode; i.e., the maximum depressing force is fixed during finger typing. Under such a mode, the depression magnitude of each typing depends mainly upon the resistance force provided by the loading rubber 101. That is to say that the lowest depression position by the finger depends mainly upon the reaction force of the key 200.
FIG. 2 illustrates a conventional pneumatic key durability testing apparatus. The apparatus as shown has a plurality of air cylinders 21 mounted on a fixed rack 20. Each of the air cylinders 21 can communicate with a common air compressor (not shown in the figure) through a respective hose 23. While in use, the air compressor pumps compressed air into each air cylinder 21 to move the respective piston rod 211 downward for further depressing the respective key 200. In each air cylinder 21, a spring (not shown in the figure) is included to push the piston rod 211 upward for completing a testing cycle, after the pressure provided by the air compressor is removed.
It is obvious that this pneumatic kind of testing apparatus requires an air compressor to perform the reciprocal test forcing. Thus, the equipment cost of the testing apparatus is much higher than that for the previous apparatus. Moreover, the usage of only a single air compressor induces an evenness problem upon distribution of application air pressure, because a plurality of air cylinders at different distances need to be fed evenly for achieving a better testing outcome. Furthermore, the spring located inside the air cylinder 21 for providing lifting force may make the downward air pressure less evenly and less accurately while being applied upon the key. The spring is also prone to resilient fatigue after long testing time of repeated reciprocal movement, and to making downward pressure applied upon the key greater than the preset value. All these disadvantages do inevitably lead to negative impacts upon test accuracy.
It is an object of this invention to provide an air buffer tape apparatus for key durability testing for effectively simulating actual key stroke operation to obtain accurate test results.
It is another object of this invention to provide an air buffer type apparatus for key durability testing that mimics accurate finger performance by using a closed air chamber to communicate with a pressure chamber located at the depressing end with a predetermined fixed displacement.
It is a further object of this invention to provide an air buffer type apparatus for key durability testing that mimics constant typing pressure situation by using an elastic closed air chamber to provide a constant pressure upon a piston rod for further applying constant pressure on the key.
The air buffer type apparatus for key durability testing according to this invention aims mainly at performing durability test upon a keyboard having a plurality of keys. It includes a driving unit for fixed displacement control, a buffer unit and a depressing unit.
The buffer unit is a closed air chamber which maintains substantially a constant internal air pressure to provide a buffer space for any key depression.
The depressing unit, driven by the driving unit, includes a plurality of air cylinders, in which each air cylinder communicates with the buffer unit through a hose to utilize the buffer unit as a buffer mechanism for the key-depressing operation. Further, each of the air cylinders has a pressure chamber which is formed in a cylinder and links to the buffer unit by means of the hose, and a depressing head in the form of a piston with a piston rod extending outside the air cylinder for depressing the key.
When in operation, the driving unit drives the depressing unit and the air cylinders to move reciprocally up and down at a constant displacement. During the up and down movement, the depressing head can press the key with a constant pressure. During the testing even at the point that the key poses at its lowest position, a substantial constant pressure for the depressing head to press upon the key can be still maintained by the buffer unit that can absorb any possible pressure variation during the testing. Under such an arrangement, this apparatus of the present invention may perform effective and accurate key stroke simulation.
In an embodiment of the present invention, the driving unit can be a cam driving mechanism.
In an embodiment of the present invention, the buffer unit may include at least one buffer zone which provides a total volume larger than the total volume difference of the air cylinders during the testing.
In an embodiment of the present invention, the buffer unit may also include a compression means for pumping compressed air into the buffer unit when the air pressure therein falls below a preset level.
In an embodiment of the present invention, the buffer unit may further include a pressure relief valve for releasing air pressure in the buffer unit.